Make a miniature storm glass barometer to wear as a pendant on a necklace. (Eigenes Foto)

The storm glass was one type of barometer used by Admiral Fitzroy of the HMS Beagle (of Darwin Expedition fame). Changes in atmospheric conditions affect chemical equilibrium inside the glass, causing crystals to precipitate and vanish. While the device isn’t as reliable as Doppler radar when it comes to predicting the weather, it’s a lot of fun to make and observe. I’ve had instructions for making a storm glass barometer over at About.com Chemistry for many years, but you can also miniaturize the device to measure changes in other conditions. For example, if you wear a small sealed storm glass around your neck as a pendant, you can use it as an extra-awesome geeky mood predictor.

Storm Glass Pendant Materials

Okay, let’s be honest here. These are not chemistry supplies you’re going to pick up at Wal-mart or the hardware store. Unless you work in a well-stocked or ancient chemistry lab, you’re going to have to shop around online for camphor. Some of the other ingredients you can make yourself, if you’ve a mind.

You’re looking for natural camphor, which looks like a white or cream-colored waxy solid. This is by far the trickiest chemical to find. The others are easily obtained or made at sufficient purity for this project. Note some people have reported having excellent luck using much less camphor than 10 grams.

Make the Storm Glass Barometer Solution

These chemicals don’t naturally dissolve together, which is the scientific “magic” behind the functioning of the storm glass. Specifically, camphor won’t dissolve in water, but it will dissolve in ethanol. The salts (potassium nitrate and ammonium chloride) dissolve in water, but not so much in ethanol. Ethanol and water are miscible, so you can combine the two solution.

So, you need to make two separate solutions and then mix them together.

Mix together the ethanol and camphor. You’ll probably need to apply gentle heat to coax the camphor into the ethanol. Remember, ethanol is flammable! My advice is to set the container on a hot plate set on low heat or better yet, in a hot water bath. Do not apply a direct flame!

In a separate container, dissolve the potassium nitrate and ammonium chloride in distilled water. You can use warm water if you want, but the salts should dissolve readily in room temperature water.

Now for the cool part! Gradually add and stir the aqueous salt solution into the camphor solution. You’ll see precipitation occur as you mix the chemicals.

You want a clear solution. If your solution is not clear, apply gentle heat to dissolve any precipitates in the solution.

This solution would work perfectly fine for a weather prognosticating storm glass barometer, but if you want to see crystals form and dissipate near body temperature, you’ll probably need to tweak the recipe.

Pour the solution into your vials, but allow the solution to cool to near-body temperature before stoppering or sealing the container. According to a chart I found online, you’re aiming for around 33 °C or 91 °F. possibly a bit cooler if the pendant won’t be in direct skin contact. So, get the solution in the vials near the target temperature. If you see a lot of crystallization, you can add a tiny bit of ethanol to dissolve the crystals.

Seal one of the vials and see what you’ve got. It may work perfectly the first time, but don’t fret if it doesn’t.

Storm Glass Troubleshooting

The size and shape of the bottle will affect the functioning of a storm glass pendant. (Thomas Durka)

Add a bit more solvent (usually the alcohol and not the water) if too many crystals form. If you can’t get any crystallization at all, evaporate off some solvent. If you still don’t get crystals, add more of either the camphor or the salts (usually the salts work in equal masses).

The size and shape and head space (empty space) of your container affects the performance of the storm glass. You could try using a larger/smaller or different shape of container. You could fill the vial more or less full.

It’s a really good idea to write down exactly what chemicals you used (manufacturer), the quantities you used, the size/shape/material of the vial and the volume of liquid. These notes will help you in case experimentation is needed.

See How To Make the Storm Glass Solution

Here’s a video showing how to make a storm glass. Seems easy enough, right?